Printers in a so-called ink jet system where a liquid or fused solid ink is ejected from nozzle, slit, porous film or the like to make recording on paper, cloth or film are advantageous in that the printer is compact, inexpensive and noiseless. Accordingly, a large number of printers in this system are commercially available. Among these, a so-called piezo-ink jet system using a piezoelectric element and a so-called thermal ink jet system of forming droplets by the action of heat energy and thereby performing recording have many advantages, for example, capabilities of high speed printing and high resolution.
Conventional ink jet recording systems commonly employs an ink using a water-soluble dye. This ink has excellent long-term storage stability but has a problem in the water resistance and light fastness. On the other hand, an ink using a pigment exhibits excellent resistance against water or light and at the same time, ensures formation a high density image free of blurring. Accordingly, this ink is very promising and a large number of proposals have been made thereon and put into practice in recent years.
For example, JP-A-56-147871 proposes a recording solution comprising an aqueous medium containing a pigment, a polymer dispersant and a nonionic surfactant, U.S. Pat. Nos. 5,085,698 and 5,221,334 propose to use an AB or BAB block copolymer as a dispersant for the pigment, and U.S. Pat. No. 5,172,133 proposes to use a specific pigment, a specific water-soluble resin and a specific solvent. On the other hand, with respect to the method for dispersing a pigment using no dispersant, U.S. Pat. No. 5,571,311 proposes a method of introducing a substituent containing a water solubilizing group into carbon black, JP-A-8-81646 proposes a method of polymerizing a water-soluble monomer or the like on the surface of carbon black, and JP-A-8-3498 proposes a method of acidifying carbon black.
In general, an ink using a pigment is known to have a problem in the image fixing property. A method of elevating the ink fixing property by adding a surfactant into an ink is described in JP-A-55-65269, however; if this method is applied to an ink using a pigment, although the image fixing property may be improved, there arises a problem that a sufficiently high image density cannot be obtained.
JP-A-5-202328 describes a method of insolubilizing a dye or the like by the action of a liquid containing a multivalent metal salt, however, if this method is applied to an ink using an ink, although a high image density may be obtained, there arises a problem that the image fixing property deteriorates.
Furthermore, JP-A-8-193175 describes a method of combining a liquid composition containing a cationic substance and a nonionic substance with an ink containing an anionic compound, where the coloring material is aggregated by the cationic substance, the aggregate produced is adsorbed to a nonionic polymer substance, and thereby the coloring material is fixed in the recording medium. According to this method, both the fixing property and the optical density can be satisfied simultaneously. JP-A-8-197840 and JP-A-9-286940 described methods similar to this method.
However, none of these methods can succeed in obtaining a recording material having high optical density, excellent image fixing property, good long-term storage stability and superior jetting stability.